The use of seal assemblies in down-hole oil field applications is known. In one particular application, an oil drilling completion, and/or measurement tool is run down into an oil well lined with casing, and the equipment includes an annular groove within which an annular seal assembly is positioned to seal the space between the inner diameter of the casing and the outer diameter of the equipment. In the prior art, such a seal assembly typically comprised an annular seal element having annular coil springs molded into the two corners of the outer diameter (in toroidal cross-section), where the springs themselves act to prevent extrusion of the seal element in the region of such outer diameter corners.
Such a prior art seal assembly was found to work well under lower pressures and lower temperatures, for example up to 5,000 psi and 250.degree. F. However, it is now typical in down-hole oil fields apparatus to have higher pressures and higher temperatures, on the order of 20,000 psi and 450.degree. F., respectively. As one skilled in the art will appreciate, at such higher temperatures and pressures, the seal element of such prior art seal assembly, which is typically a rubber-like material, tends to flow and extrude through the springs, thereby resulting in a loss of seal element material and eventual seal failure.
Accordingly, it has been proposed to employ as a seal assembly in the aforementioned down-hole oil field application a T-shaped seal element (in toroidal cross-section) and a pair of annular back-up or anti-extrusion elements, one on each axial side of the T-shaped seal element. Such proposed T-seal seal assembly is known in the prior art and has been used in one form or another in other applications such as hydraulic or pneumatic systems for both rod- and piston-type seals. Generally, each back-up element is positioned adjacent the T-shaped element and the contact point thereof such that when higher pressure is applied to the opposite axial side of the T-shaped seal element, the respective back-up element prevents extrusion of the T-shaped seal element, in the area of such contact point.
However, it has been found that such prior art T-seal seal assemblies do not work well in the previously described high temperature and high pressure environment of a down-hole oil field application. In particular, it has been found that one or both of the back-up elements tends to become displaced from the T-shaped seal element, thereby failing to provide the desired back-up function such that the T-ring seal assembly eventually fails. Accordingly, a need exists for a T-ring seal assembly that works well under high pressure and high temperature, whereby the back-up elements do not become displaced with regard to the T-shaped seal element.